Vertical structures such as vertical high power transistors and trench capacitors are becoming more prevalent in integrated circuits to reduce area. Trench capacitors and vertical transistors formed on the sidewalls of trenches occupy significantly less area than planar capacitors and planar transistors which are built on the semiconductor surface.
A major challenge in building vertical capacitors and vertical transistors is to grow high quality, uniform dielectric on the sidewalls and bottom of the trenches. This becomes increasingly difficult as the trenches get narrower and deeper. The trench etch may cause roughness on the trench sidewalls and may cause sharp corners at the bottom of the trenches. The electric field may be enhanced at rough spots and sharp corners causing increased leakage current through the trench oxide accelerating the wear out and reducing the lifetime of the dielectric.
In addition the growth rate of silicon dioxide is different for the different crystal planes exposed on the trench sidewalls and trench bottom. The ratio of silicon dioxide thickness on a trench sidewall to the thickness on the bottom of the trench is typically about 1.7. Nonuniformity in the dielectric thickness degrades the performance of the vertical MOS transistors and trench capacitors.